This project was initiated to analyze, both qualitatively and quantitatively, changes in total cellular protein patterns during cellular senescence using the technique of quantitative two- dimensional polyacrylamide gel electrophoresis. A human endothelial cell culture system has been developed which allows one to study changes in cellular polypeptide expression in presenescent and senescent human umbilical vein endothelial cells (HUVEC) and to follow changes in cellular phenotype and polypeptide expression following treatment with a variety of biological growth factors. Two-dimensional polyacrylamide gel electrophoresis of (35-S)-methionine-labelled polypeptides of young presenescent (16 population doublings) and old senescent (55 population doublings) human endothelial cells treated with 12-0-tetradecanoylphorbol-13-acetate (TPA), recombinant gamma-interferon (gamma-IFN), and tumor necrosis factor (TNF) revealed the expression of polypeptides unique to each biological response modifier and also unique to senescence. Presenescent HUVEC express 13 polypeptides that are not expressed in senescent cells and senescent human endothelial cells express 9 polypeptides that young cells do not express. Furthermore, TPA and gamma-IFN revert the expression of a number of polypeptides which are unique to presenescent and old senescent cells.